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Oracle SQL references describes partition:
Partitioning allows a table, index, or index-organized table to be subdivided into smaller pieces, where each piece of such a database object is called a partition. Each partition has its own name, and may optionally have its own storage characteristics.
Then I have a question, if I only have one hard disk, the partition table can be placed only on a disk. Can a partition table improve performance?
Partitioning on a single disk can still help for some queries. For instance, Oracle can do partition-pruning: this is the ability to select from only a subset of all partitions for a query.
Suppose that you have a table that contains data from the last 12 months. If you want to query some total and average over one particular month, Oracle will probably need to FULL SCAN the whole table or read a lot of data with an index. With a partitioning scheme by month, Oracle would only need to read 1/12th of the data and still be able to FULL SCAN the partition as if it were a smaller version of the big table.